What is there in 4.2 that appeals to you ...?
From what I've read, the only thing of interest to me is Photo Sphere. We already have DLNA, Swype, NFC, Google Now. Most of what 4.2 is said to offer is already running on my M on JB-4.1. I think 4.2 is more taylored for devices that are lacking, as compared to what's already available to the M.
4.2 would be the second update to this phone, Razr-i is running 4.1, and I've read Razr M-HD may be released running 4.1 ... I don't think 4.2 has enough device-benefit to the M for Motorola to invest in the cost of another incremental OTA release (soak time, OTA Deployment, etc.).
I think the significant question will be; will Motorola give the M users Key Lime Pie (v5.0) as OTA option. I hope the 2012 Google acquisition of Motorola Mobility (handheld phones lines) see fit to continue the Razr line into the future and not vest into "Google Phones" and ignoring future support of the existing Razr line!